At peak time, the runway(s) at an airport are often the capacity limiting function and their use needs to be optimised. Optimisation of runway use during busy and peak load times typically is at is at the cost of efficient aircraft operation. Traditional air traffic control (ACT) practice allows aircraft to arrive in the vicinity of the destination airport at a time of their choosing, and/or having made use of holding, vectoring, and path adjustment in the vicinity of the destination. ATC queues aircraft in a sequence for landing. ATC use Holding and Vectoring (path length for adjustment) to feed the aircraft to the runway with the desired spacing. The aircraft are spaced relative to each other (“using relative time”). The use of Holding at low altitude is fuel inefficient; Vectoring precludes the use of the aircraft Flight Management System (FMS) to optimise aircraft descent profile.
Precision navigation, such as Required Navigation Performance (Arrival) procedures (RNPs) provide the opportunity to improve efficiency of aircraft and fuel use. At high density airports during periods of peak traffic density, the use of Holding and Vectoring, or the controlling of aircraft arrivals via relative time (as opposed to absolute time) sequencing often denies an aircrafts FMS the opportunity to optimise trajectories, including RNP procedures to optimise aircraft operation.